Modern UV-lithography is searching for new highly parallel writing concepts. Spatial light modulation with optical MEMS devices offers such possibilities. An SLM chip may comprise a DRAM-like CMOS circuitry with several million individually addressable pixels on top. Said pixels are deflected due to a difference in electrostatic force between a mirror element and an address electrode. A pattern generator using an SLM is described in U.S. Pat. No. 6,373,619, which is assigned to the same assignee as this invention. U.S. Pat. No. 6,373,619 discloses in short a small field stepper, which exposes a series of images of the SLM. A workpiece is arranged on a stage, which is continuously moving and a pulsed electromagnetic radiation source (which could be a pulsed laser, a flash lamp, a flash from a synchrotron light source, etc) flashes and freezes an image of the SLM on the workpiece. The SLM is reprogrammed with a new pattern before each flash so a contiguous image is composed on the workpiece.
In the past, integrated circuits have been manufactured more or less solely by using a number of masks or reticles comprising a pattern of a layer in said integrated circuit. In today's integrated circuits the number of layers could be larger than 30. Said Masks or reticles may be prepared in lithographical manner by using for example electron beams or laser beams for exposing a layer of material sensitive for the type of beam chosen. The mask material, which is most commonly transmissive, may have attached on top of one of its sides a thin layer of opaque material. In said thin layer of opaque material the pattern of one layer of said integrated circuit may be created. The mask has typically N times larger pattern than the pattern to be printed on the semi-conducting substrate for forming said integrated circuit. The reduction in size may be performed in a stepper or a scanner, which may use the mask(s) for forming said integrated circuit.
More recently, the need to manufacture integrated circuits by means other than using a conventional mask has developed for a number of reasons, for example the price of manufacturing mask(s) has increased due to its complexity to manufacture, small-scale development requiring only a small number of integrated circuits, etc.
Unfortunately, all of the present known techniques for forming integrated circuits without using conventional masks or reticles have drawbacks and limitations.
For example, most direct-writers known in the art are based on electron beams, typically so called shaped beams, where the pattern is assembled from flashes, each defining a simple geometrical figure. Other systems are known which use raster scanning of Gaussian beams. By using a conventional mask writer, which uses beams of electrons or laser beams for forming the pattern on a workpiece, may be limited to relatively low scanning speeds, and, perhaps worst of all, may only scan a single dimension.
SLM writers disclosed in other patent applications, such as WO 01/18606 and U.S. patent application Ser. No. 09/954,721 (now U.S. Pat. No. 7,302,111), by one of the assignees of the present invention and hereby incorporated by reference, are related to raster scanning in the sense that it permits a bitmap pattern, but distinct by printing an entire frame of pattern in one flash instead of building the pattern from individual pixels.
A spatial light modulator (SLM) comprises a number of modulator elements, which can be set in a desired way for forming a desired pattern. Reflective SLMs may be exposed to any kind of electromagnetic radiation, for example DUV or EUV for forming the desired pattern on the mask or any other workpiece.
A direct-writing pattern generator for writing certain layers in a semiconductor design directly from data would have a high value to the industry. However, the complexity of modern chips is extremely high and getting higher by every new technology generation. The direct-writer must write the complex pattern not one, but millions of times on a 300 mm wafer.
A direct write machine that may expose LCD large area substrates must have a write time of around one minute in order to be competitive. This time is very short compared to the “day” needed to make a mask. A writing speed is therefore very large (1000× or more) compare to present technology. One major obstacle is the stage speed, which must have a speed that is “too large”. This may however be avoided by writing in a large width, but this may require a large number of optical channels and lenses which both increases the cost and complexity.
The mechanical motion may also be a problem with large stage speeds as the mass increases while the time allowed for the turn around decreases drastically. The shorter turnaround time and the increased forces may also induce grater vibrations and resonance at higher frequencies in the mechanical structure. There may also be the ever larger problem of mechanical systems to settle properly before start writing.
An increased turnaround time also consumes valuable time needed for the writing itself.